Sound-recording system



y 7, 1929' N. H. HOLLAND 1,711,681

SOUND RECORDING SYSTEM Filed April 50, 1926 lm/emar: lair/2200 7/0//dfid Patented May 7, 1929.

UNITED STATES PATENT OFFICE.

NEWMAN H. HOLLAND, MONTCLAIR, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

SOUND-RECORDING SYSTEM.

Application filed April 30,

This invention relates to phonographs and more particularlv to phonographs for makmg sound records.

An object of this invention is to provide a means for damping the movement of the recording elements of a phonograph so that distortion in the record is practically eliminated.

,A further object is to provide a direct monitoring arrangement.

It has been found in making records either by means of the usual mechanical unit or the electromagnet unit that there is a certain amount of distortion in the record. There are several causes for this, one being that the energy required to make the record varies with the frequency and to a lesser extent with the amplitude of the vibrations to be recorded. This variation in turn depends upon the elasticity and mass of the moving elements.

Another cause, and from the magnitude of its effects the more dominant one, is the surplus energy stored in the system over that required for recording. This surplus energy must be dissipated and, in the recording systems now in use, dissipation takes place through the recording elements, mainly the stylus arm. The dissipation of the surplus energy of the system manifests itself by main- I taining the stylus actuated for a longer time than the actual sound vibrations endure. This naturally causes distortion.

In accordance with the present invention the surplus stored energy is dissipated through a medium other than the recording elements. More specifically the dissipating medium is a horn having a diaphragm directly connected to the recording stylus.

Such av horn must have a straight line resistance characteristic, or, in other words, the

horn must offer constant opposition to motion at frequencies within the audible range. Horns of this type are generally rather large but one which fulfills the foregoing re uirement and which is smaller in size and ence more practical, is that known as the exponential horn which is disclosed in the copending application of Paul B. Flanders, Serial No. 7 59,182, filed December 31, 1924.

Not only is the surplus energy dissipated in horns of the above type but the distortion due to the variation in energy at different frequencies and amplitudes is also greatly diminished. These horns also serve as indicators of 1929. Serial No. 105,746.

the movements of the members impressing the sound vibrations on the record blanks.

The following description covers the invention as applied to a phonograph recorder using an electromagnetic unit, such an arrangement being schematically represented in the attached drawing.

A record plate 5 upon which the vibrations are to be impressed is acted upon by any approved type of needle 7 held in the stylus bar 6 which is actuated by the armature 8 of the electromagnetic unit 9.

The manner of actuating the armature 8 of the electromagnetic unit is well understood and consists in impressing currents in the windings 10 of the unit. These currents are produced in the secondary winding 11 of a transformer 12 from a modulated direct current in the primary winding 13 of the transformer; the direct current being modulated by the transmitter unit 14. The direct cur rent may be supplied by dry cells or other direct current source 15 in the closed circuit with the transmitter and primary winding of the transformer.

The diaphragm 17 of the horn is directly connected to the stylus by means of rigid rod 16. The horn 18 is preferably the special type mentioned above and has a taper which follows the exponential law and a mouth opening, the area of which is equal to that of a circle having a diameter not greater than one- 5 third nor less than one-quarter of the wave length at the cut-off frequency of the horn.

With this arrangement the energy absorbing effect of the horn is such that the stylus follows very faithfully the sound vibrations so impressed on the transmitter 14 and practically no distortion is present in the record so made. In the same way the inertia effects of the moving parts are suppressed.-

In cases Where the transmitter unit is siton uated ata distance from the recording apparatus this horn serves as an indicator of the actual stylus vibration and is therefore a considerable improvement over those types of monitoring arrangements in which the unit for monitoring is included in the system at some point other than at the stylus.

What is claimed is:

1. A sound recording system, comprising a translating device, a vibrating element re- 106 sponsive to said device, a recording stylus attached to the element, a horn, a diaphragm in said horn and a member rigidly connecting said, diaphragm to said stylus, said horn and diaphragm offering constant opposition to vibrations having frequencies in the audible range. i

2. A sound recording system, comprising a translating device, a vibrating element responsive to said device, a recording stylus attached to the element, a horn having a taper which varies according to the exponential law, a diaphragm in said horn and -a' quarter of the wave length at the cut-off frequency of the horn, a diaphragm permanently fixed to said horn and a rigid rod connecting said stylus and said diaphragm.

4. In a phonograph recording system, a translating device, a vibrating element 'responsive to said device, a recording stylus attached to the element, and a horn type indicator actuated by said recording stylus, said horn having a taper which follows the exponential law.

5. An audible indicating device for phonographic recording systems, comprising a recording stylus, a horn and a diaphragm attached to said horn, and actuated by said recording stylus, said horn having a taper which follows the exponential'daw and having a mouth opening equal in area to that of a circle having a dlameter not greater than one-third nor less than one-quarter of the wave length at the cut-off frequency of the horn.

6. A method of eliminating distortion in sound recording which consists of dissipating the surplus energy stored in the recording system through a horn type loud speaker coupled to the moving system of the recorder, said horn offering constant mechanical opposition to vibrations having frequencies in the audible range.

In witness whereof, I hereunto subscribe my name this 29 day of April A. D., 1926.

NEWMAN H. HOLLAND. 

